A polycarbonate-based resin is a polymer excellent in transparency, heat resistance, and impact resistance and is widely used at present as an engineering plastic in the industrial field.
As a method for producing the polycarbonate-based resin, a method involving allowing an aromatic dihydroxy compound such as bisphenol A, and phosgene to react directly with each other (interfacial polymerization method) is known as a method of producing a high-quality polycarbonate.
As a method for industrially producing a polycarbonate by an interfacial condensation polymerization method, in general, there is adopted a method involving bubbling phosgene into an alkali aqueous solution of a bisphenol to form a polycarbonate oligomer having a reactive chloroformate group, and further mixing the polycarbonate oligomer and the alkali aqueous solution of the bisphenol to perform a condensation reaction (polymerization reaction) in the presence of a polymerization catalyst such as a tertiary amine. From the viewpoints of solubility, handleability, and the like, methylene chloride is mainly used as the water-insoluble organic solvent on an industrial scale.
The bisphenol as a raw material monomer is typically supplied after having been dissolved in aqueous sodium hydroxide. Accordingly, the sodium hydroxide concentration of the resultant solution is adjusted to a predetermined value in a dissolution tank for dissolving the bisphenol in the aqueous sodium hydroxide, and the solution is fed to each of a step of producing the polycarbonate oligomer and a step of producing a polycarbonate copolymer (see Patent Document 1). The concentration of the bisphenol and the concentration of sodium hydroxide at this time are extremely important in terms of the control of the reaction for the production of the polycarbonate oligomer. Meanwhile, upon production of the polycarbonate copolymer from the oligomer, the optimum sodium hydroxide concentration differs from that of the solution of the bisphenol in the aqueous sodium hydroxide used in the production of the polycarbonate oligomer, and hence the aqueous sodium hydroxide is typically further added in a supply tube immediately in front of a reactor for polymer production.
It should be noted that, among the polycarbonate-based resins, a polycarbonate-polyorganosiloxane polymer (hereinafter sometimes referred to as “PC-POS”) has been attracting attention because of its high impact resistance, high chemical resistance, and high flame retardancy, and the polymer has been expected to find utilization in a wide variety of fields such as the field of electrical and electronic equipment and the field of an automobile. As a method of producing the PC-POS, there is known a method involving allowing a dihydric phenol-based compound and phosgene to react with each other to produce a polycarbonate oligomer, and polymerizing the polycarbonate oligomer with a polyorganosiloxane in the presence of methylene chloride, an alkaline compound aqueous solution, a dihydric phenol-based compound, and a polymerization catalyst (interfacial polycondensation method) (see Patent Document 2).